The proposed study is designed to evaluate the safety, efficacy, and pharmacokinetics of paroxetine in children with major depression or obsessive compulsive disorder. Our goal is to develop some rational dosing recommendations for paroxetine in this patient population and to understand the biologic basis for the expected interindividual differences in dosing requirements. Subjects are still being accrued. Thirty patients have been enrolled, 25 have completed the study.